000
FXUS63 KDMX 111000
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
400 AM CST Sun Feb 11 2018
.SHORT TERM.../Today through Tonight/
Issued at 358 AM CST Sun Feb 11 2018
Bottom Line Up Front...
Ongoing snow, primarily across our eastern to southeastern CWA,
will quite plausibly be the last widespread, impactful precip
until next weekend.
Ongoing Precip...
Radar analysis coupled with sfc obs shows precip beginning to
move east of the DMX CWA, weakening as it does so. Trend supported
by hi-res models as they all depict frontogenetical forcing
through the DGZ/ascent processes waning and moving east as well.
By 12z to 15z Sun, forcing and precip should be east of our area.
Rest of Today and Tonight...
Large-scale subsidence overspreading Iowa very quickly behind this
system as a weak sfc high approaches southern Iowa via Kansas. Cross-
section analysis over time also shows prominent dry air entrainment
overspreading Iowa which should set us up for clear blue skies by the
afternoon and into tonight. Overall air mass today fields similar
temps to yesterday, with 850mb temps near -10C to -13C. With the
sun, temperatures should be a solid 5 to 10 degrees warmer today
across the CWA... and of course, tonight will be cooler as
radiational cooling will occur more readily than this morning.
.LONG TERM.../Monday through Saturday/
Issued at 358 AM CST Sun Feb 11 2018
Monday and Tuesday...
On the heels of the small sfc high that cruises through Iowa
Sunday, a 1045mb sfc high will punch eastward across the Dakotas and
into the Great Lakes region... making it to Lake Michigan by 12z
Tue and the eastern U.S. by Wednesday. For flurry/light snow
chances, There still remains some disagreement with the GFS versus
the other medium-long term models. Several GFS ensemble
perturbations bring a ribbon of precip across NW Iowa Tuesday
morning. The GFS is still showing a pocket of saturation through
the DGZ that is phased with a broad area of low-level moisture
flux convergence. The challenge is with 850mb temps back up to the
-2C to -4C range by Tuesday, the saturated DGZ is 5km off the sfc.
Fcst soundings show bkn st possible less than 1 km off the deck,
and dry air in between, which is too much difference for seeder-
feeder processes to yield precip. So, have opted to leave
Tuesday dry at this time.
Wednesday...
Sensible weather impacts return for Wednesday as WAA takes over the
state. Confidence decently high as models showing good convergence
and run-to-run consistency on WAA solution. 850mb temps likely to
make it to the +7C to +10C range, and more importantly, sfc
dewpoints above 32 to overspread iowa from south to north. Fcst
soundings across our area shows very strong inversion in place. In
all, a classic setup for fog to be trapped in the lowest 0.5 km
or so via melting snow. Have lowered temps vs guidance, and believe
current fcst high temps could still be 5 or degrees too warm
along and north of I-80.
Thursday and Beyond...
A shortwave looks to ride along the US/Canadian border under the
influence of the longwave trough from the Hudson Bay low. An
attendant cold front will pass through the upper Midwest sometime
Thursday which should bring an end to the warm temperatures.
Still some timing issues as the GFS is a notably faster than the
ECMWF. Regardless the model, Dry air and a lack of organized forcing
suggest this will be a largely precip-free fropa. Large-scale
subsidence and dry air entrainment hinted at behind this fropa
should clear out skies rapidly. Strong winds likely Thursday into
Friday, but with a pressure gradient of only 3mb/115 km or so, winds
should remain well below advisory criteria. Confidence into next
weekend next to nil as long-range models have little run-to-run
consistency.
&&
.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1053 PM CST Sat Feb 10 2018
Bands of snow will result in periodic IFR conditions at DSM and
OTM in the next several hours, with conditions improving rapidly
as the snow moves out early Sunday morning. By 12Z these sites
will be VFR and along with the northern terminals, will remain VFR
through the remainder of the TAF period.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM CST early this morning for
IAZ075-083>086-092>097.
&&
$$
SHORT TERM...Kotenberg
LONG TERM...Kotenberg
AVIATION...Lee